1. 0x01 Itertools
1.1. Infinite Iterators
无限迭代
count(10, 1) --> 10 11 12 13 14 ...
cycle('ABCD') --> A B C D A B C D ...
repeat(3) --> 3 3 3 3 ... repeat(4, 3) --> 3 3 3
1.2. Iterators terminating on the shortest input sequence
处理输入迭代
chain('ABC', 'DEF') --> A B C D E F
compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F
dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1 # 跳过头部符合条件的元素
takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4 # 保留头部符合条件的元素
groupby(['aa', 'abc', 'abcd', 'ab', 'ccf'], len) --> ['aa', 'ab'] ['abc', 'ccf'] ['abcd']
ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9
ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8
islice('ABCDEFG', 2, None) --> C D E F G
imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000
starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000
tee() it, n it1, it2, ... itn splits one iterator into n
izip('ABCD', 'xy') --> Ax By
izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
1.3. Combinatoric generators
组合生成
product('ABCD', repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD
permutations('ABCD', 2) AB AC AD BA BC BD CA CB CD DA DB DC
combinations('ABCD', 2) AB AC AD BC BD CD
combinations_with_replacement('ABCD', 2) --> AA AB AC AD BB BC BD CC CD DD
- chain
chain(*iterables) --> chain object
Return a chain object whose .next() method returns elements from the first iterable until it is exhausted, then elements from the next iterable, until all of the iterables are exhausted.
- combinations
combinations(iterable, r) --> combinations object
Return successive r-length combinations of elements in the iterable.
combinations(range(4), 3) --> (0,1,2), (0,1,3), (0,2,3), (1,2,3)
- combinations_with_replacement
combinations_with_replacement(iterable, r) --> combinations_with_replacement object
Return successive r-length combinations of elements in the iterable allowing individual elements to have successive repeats.
combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC
- compress
compress(data, selectors) --> iterator over selected data
Return data elements corresponding to true selector elements. Forms a shorter iterator from selected data elements using the selectors to choose the data elements.
- count
count(start=0, step=1) --> count object
Return a count object whose .next() method returns consecutive values.
Equivalent to:
def count(firstval=0, step=1):
x = firstval
while 1:
yield x
x += step
- cycle
cycle(iterable) --> cycle object
Return elements from the iterable until it is exhausted. Then repeat the sequence indefinitely.
- dropwhile
dropwhile(predicate, iterable) --> dropwhile object
Drop items from the iterable while predicate(item) is true. Afterwards, return every element until the iterable is exhausted.
- groupby
groupby(iterable[, keyfunc]) -> create an iterator which returns (key, sub-iterator) grouped by each value of key(value).
- ifilter
ifilter(function or None, sequence) --> ifilter object
Return those items of sequence for which function(item) is true. If function is None, return the items that are true.
- ifilterfalse
ifilterfalse(function or None, sequence) --> ifilterfalse object
Return those items of sequence for which function(item) is false. If function is None, return the items that are false.
- imap
imap(func, *iterables) --> imap object
Make an iterator that computes the function using arguments from each of the iterables. Like map() except that it returns an iterator instead of a list and that it stops when the shortest iterable is exhausted instead of filling in None for shorter iterables.
- islice
islice(iterable, [start,] stop [, step]) --> islice object
Return an iterator whose next() method returns selected values from an iterable. If start is specified, will skip all preceding elements; otherwise, start defaults to zero. Step defaults to one. If specified as another value, step determines how many values are skipped between successive calls. Works like a slice() on a list but returns an iterator.
- izip
izip(iter1 [,iter2 [...]]) --> izip object
Return a izip object whose .next() method returns a tuple where the i-th element comes from the i-th iterable argument. The .next() method continues until the shortest iterable in the argument sequence is exhausted and then it raises StopIteration. Works like the zip() function but consumes less memory by returning an iterator instead of a list.
- izip_longest
izip_longest(iter1 [,iter2 [...]], [fillvalue=None]) --> izip_longest object
Return an izip_longest object whose .next() method returns a tuple where the i-th element comes from the i-th iterable argument. The .next() method continues until the longest iterable in the argument sequence is exhausted and then it raises StopIteration. When the shorter iterables are exhausted, the fillvalue is substituted in their place. The fillvalue defaults to None or can be specified by a keyword argument.
- permutations
permutations(iterable[, r]) --> permutations object
Return successive r-length permutations of elements in the iterable.
permutations(range(3), 2) --> (0,1), (0,2), (1,0), (1,2), (2,0), (2,1)
- product
product(*iterables) --> product object
Cartesian product of input iterables. Equivalent to nested for-loops.
For example, product(A, B) returns the same as: ((x,y) for x in A for y in B). The leftmost iterators are in the outermost for-loop, so the output tuples cycle in a manner similar to an odometer (with the rightmost element changing on every iteration).
To compute the product of an iterable with itself, specify the number of repetitions with the optional repeat keyword argument. For example, product(A, repeat=4) means the same as product(A, A, A, A).
product('ab', range(3)) --> ('a',0) ('a',1) ('a',2) ('b',0) ('b',1) ('b',2)
product((0,1), (0,1), (0,1)) --> (0,0,0) (0,0,1) (0,1,0) (0,1,1) (1,0,0) ...
- repeat
repeat(object [,times]) -> create an iterator which returns the object
for the specified number of times. If not specified, returns the object endlessly.
- starmap
starmap(function, sequence) --> starmap object
Return an iterator whose values are returned from the function evaluated with an argument tuple taken from the given sequence.
- takewhile
takewhile(predicate, iterable) --> takewhile object
Return successive entries from an iterable as long as the predicate evaluates to true for each entry.
- tee
tee(iterable, n=2) --> tuple of n independent iterators.